Automatic tool position compensating system for a numerically controlled machine tool

ABSTRACT

IN A NUMERICALLY CONTROLLED MACHINE TOOL HAVING A TOOL SUPPORT SLIDE, A MULTIPLE TOOL TURRET, A CONTROLLER AND A MEASURING ELEMENT, A RING GAUGE IS MOUNTED ON THE MAIN SPINDLE OF SAID MACHINE TOOL COAXIALLY THERETO SO THAT THE DEVIATIONS OF SAID MAIN SPINDLE IN X AND Z DIRECTIONS MAY BE ACCURATELY MEASURED AND COMPENSATED FOR. TO DO THIS, THE MEASURING ELEMENT UTILIZES THE OUTER PERIPHERAL SURFACE AND THE INWARDLY FACING END SURFACE OF SAID RING GAUGE AS THE REFERENCE OR STANDARD POSITIONS IN X AND Z DIRECTIONS, RESPECTIVELY. THE DEVIATIONS ARE COMPENSATED IN THE SUCCEEDING CUTTING PROCESS FOR SHIFTING THE TOOLS RESPECTIVELY, EACH IN ACCORDANCE WITH THE ERROR DETECTED, BY PARALLEL SHIFTING OF THE CO-ORDINATE AXIS OF THE TOOLS.   ALTERNATELY, THE AXES MAY BE SHIFTED ANGULARLY, OR THE PARALLEL SHIFT MAY BE COMBINED WITH THE ANGULAR SHIFT OF THE CO-ORDINATE AXES.

Sept. 20, 1971 TADAYOSHI IZUMI EI' L v 3,605,531

AUTOMATIC TOOL POSITION COMPENSATING SYSTEM FOR Filed May 12, 1969 FIG.I

A NUMERICALLY CONTROLLED MACHINE TOOL 2 Sheets-Sheet 1 +x A E C I; N

TAPE READE CONTRQLER Tadayoshi Izumi Hideo Hirokawa Wm $9M 1TAoAvosl-ulzuml 'rAL 5 t Fmdya y' 2, 1969 AUTOMATIC TOOL POSITIONCOMPENSATING SYSTEM FOR A NUMERICALLY CONTROLLED MACHINE TOOL I 2Sheets-Sheet 2 Tqdayoshi mum l'lldeo [I'irokawa Attorneys United StatesPatent 01' fice 3,fi@5,53l Patented Sept. 20, 1971 Japan Filed May 12,1969, Ser. No. 823,893 Claims priority, application Japan, Aug. 29,1968, 43/61,447, 43/61.,448 Int. Cl. B23!) 3/28 US. Cl. 82-141) 3 ClaimsABSTRACT OF THE DISCLOSURE In a numerically controlled machine toolhaving a tool support slide, a multiple tool turret, a controller and ameasuring element, a ring gauge is mounted on the main spindle of saidmachine tool coaxially thereto so that the deviations of said mainspindle in X and Z directions may be accurately measured and compensatedfor. To do this, the measuring element utilizes the outer peripheralsurface and the inwardly facing end surface of said ring gauge as thereference or standard positions in X and Z directions, respectively. Thedeviations are compensated in the succeeding cutting process forshifting the tools respectively, each in accordance with the errordetected, by parallel shifting of the co-ordinate axis of the tools.Alternately, the axes may be shifted angularly, or the parallel shiftmay be combined with the angular shift of the co-ordinate axes.

The present invention relates to numerically controlled machine tools,and more particularly, to a system in such a machine for shifting theseries of tools to compensate for errors.

When performing a cutting operation with a numerically controlledmachine tool, such as a turret lathe, it is known that the accuracy ofdimensions of the machined workpiece tends to deviate from the requireddimensions as the cutting process progresses due to variations in theposition of the cutting tool tip from the initial or basic position seton the tape reader. This deviation occurs due to the constant cuttingforce causing thermal deformation and/or progressive wear of the tooltip during the cutting operation. 'In order to avoid such deteriorationof the accuracy of dimensions, an automatic tool position compensatingsystem for a numerically controlled machine tool has been previouslyproposed in which a measuring element is provided on the tool slide ofthe machine. The measuring element carrys out a sequence of dimensionmeasuring of the necessary machine portions by command signals issuedfrom the tape reader based upon a measuring program previouslydetermined. From this measuring, the deviations from the dimensionscalled for on the control tape are detected and the detected deviationsare memorized in the controller in the form of digital values. When theworkpiece is machined, the tools having the detected deviations areshifted to compensate for their deviation each by an amount equal tothose memorized in the controller during the check time of the previouscutting operation. The detailed explanation of such a system can befound in the copending U.S. application Ser. No. 776,327, filed Nov. 18,1968.

However, it has also been found that in the continuous cutting processwhere said process is extended for a long time, there are factors otherthan the deterioration of the accuracy of dimensions due to thedeviations of the tool positions themselves as stated above that causeinaccuracies in the finished workpiece. That is, it is also inevitablethat the center line of the main spindle of the machine or that of theworkpiece displaces due to the generation of heat in the bearings,especially the main spindle bearings, meshing parts of the gears,clutches and other parts where moving parts interact to cause friction.Further, a change in the ambient temperature or change in temperature ofthe lubricating oil can cause the deleterious displacement along thecenterline. The abovementioned prior system cannot compensate for thedeterioration of the accuracy of dimension due to such a change in theposition of the center line of the main spindle or the workpiece.

SUMMARY OF THE INVENTION Accordingly, it is an object of the presentinvention to provide an automatic tool position compensating system fora numerically controlled machine tool wherein errors caused bydisplacement of the centerline of the workpiece are compensated.

It is another object of the present invention to provide such a systemwherein to avoid the occurrence of the dimensional errors of a workpiecedue to the deviation of the center of the main spindle of the machine orthe workpiece caused by the heat generation in the machine parts, thedeviations of the spindle are automatically checked and memorized orstored in a controller so that in the succeeding cutting process saiddeviations are applied to the respective tools for correction of theirrespective positions whereby the cutting process is accurately carriedout.

It is another object of the present invention to provide an automatictool position compensating system for a numerically controlled machinetool wherein there is provided an apparatus and method of avoiding theoccurrence of the dimensional errors of a workpiece due to thedisplacement of the center line of the main spindle of the machine orthe workpiece caused by the heat generation in the machine parts; thedisplacement of the center line of the main spindle being detected by ameasuring element mounted on the tool slide and in response to which theoriginal position of each tool is corrected by shifting the toolsco-ordinate axes in proportion to the displaced value whereby theaccuracy of the machined dimension is automatically compensated.

In practice, the automatic tool position compensating system of thepresent invention forms an integral part of a numerically controlledmachine tool, such as a turret lathe. When the center line of the mainspindle or the workpiece does not correctly coincide with thatoriginally set, the deviation is checked by the measuring element on thetool slide of the machine by cooperation with a ring gauge secured tothe main spindle or chuck mounted thereon. The dimensional deviations ofthe workpiece in the direction of the longitudinal axis of the mainspindle (called the Z direction) and in the transverse direction to theaxis (called the X direction) are measured at the outer peripheralsurface and the end surface of the ring gauge, which serve as standardpositions respectively. In other words, these surfaces serve as themeasuring origins of the measuring element in Z and X directions,respectively, and any deviations are detected by the measuring elementand then memorized in the controller in the form of digital valuescorresponding to respective tool deviations. The stored digital valuesof deviation are then applied to the indexing signals for the respectivetools in the succeeding cutting process to compensate or correct thepositions.

According to another aspect of the present invention, the measuringelement detects the deviations of the center line of the workpiece fromthe proper position and in response thereto in Z and X directions thecontroller shifts the co-ordinate axes of the tool in parallel withthose originally set. Alternatively, the controller shifts the axesangularly about an original center, or shifts the axes in parallel andangularly simultaneously.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and features of thepresent invention will be appreciated and become apparent as the presentdisclosure proceeds and upon consideration of the following detaileddescription taken in conjunction with the accompanying drawings whereinexemplary embodiments of the present invention are disclosed.

In the drawing:

FIG. 1 is a diagrammatical view of a numerically controlled machinetool, e.g. a turret lathe, illustrating a preferred embodiment of theapparatus and method of automatic tool position compensating systemaccording to the present invention with the workpiece held in a chuck onthe spindle;

FIG. 2 is a view similar to FIG. 1 when the machine tool is used withthe workpiece held between the spindle and tail stock; and

FIG. 3 shows a view of a portion of the workpiece in FIG. 2 on anenlarged scale.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the system shown in FIG. 1, anumerically controlled tun'et lathe A includes a cross slide -B and aturret C which has a series of tools B B B B thereon. A measuringelement D having a feeler -E is mounted on the cross slide B oppositethe turret C.

On a chuck F forming part of a chuck and spindle assembly comprised ofthe chuck -F and the main spindle S of the lathe A and on which thechuck is mounted, is mounted a ring gauge G, such mounting beingaccomplished by means of a screw H, for example. The outer peripheralsurface of the ring gauge G has a radius R and constitutes the standardmeasuring surface in the X direction or transverse to the longitudinalaxis 0. Similar- 1y, end surface (3; of the ring gauge G which is at adistance I from the base surface W of the workpiece W constitutes thestandard measuring surface in the Z direction or along the axis 0.

Assuming that, due to the various factors resulting from the continuousmachining operation for an extended time, the main spindle S deviates,e.g. +AZ and -AX in Z and X directions, respectively, then therotational center line of the main spindle S displaces from axis 0 todisplace axis 0'.

In FIG. 1, below the center line or axis 0 there is shown the halves ofthe main spindle S and the workpiece W at their initially set location,while above the center line O is shown the halves of the main spindle Sand the workpiece W repositioned due to the shifts +AZ and AX of themain spindle S in Z and X dI-e rections, respectively; such shifts beingcaused by the abovementioned causes. When the workpiece W that has beenshifted from its center of rotation (from axis 0 to axis 0) is turned ormachined according to the program from the tape reader T by the tools BB B B which have been initally precisely set so that their tip positionscoincide with those previously programmed, the radii of the cylindricalportions W and W of the workpiece W are inaccurate, as before. That is,when said workpiece W is desired to be turned to have radii r and rrespectively, the actual radii become r +AX and r -l-AX, respectively,and the distance between the ends of the workpiece W or the lengthbecomes l AZ.

Accordingly, to correct for this inaccuracy on the next cycle, the tipof the feeler E of the measuring element D is moved along a route, e.g.the dot-dash line shown in FIG. 3, to come into contact With themeasuring fundamental surfaces G and G, of the ring gauge G. This isaccomplished by giving the measuring demand values X -R and Z'+[ +lrespectively, in X and Z directions. When tht feeler E is stopped at thesurfaces G and G the deviation outputs corresponding to the deviationsAX and +AZ, respectively, are obtained.

The deviation outputs of the measuring element D thus obtained arerespectively memorized or stored at the designated positions in thedeviation memories contained in the controller N as digital values afterbeing converted by an A-D transducer. In this connection, referenceshould be made to the aforesaid copending US. application Ser. No.776,327. The controller N decodes the programmed information fed in bythe tape reader T, delivering numerical information and character ornotation information respectively to a register and a miscellaneousfunction device, both also contained in the controller N. Theinformation from in the miscellaneous function device is eitherdelivered to the outside to index the turret C or regulate therevolution of the spindle S, or delivered together with the informationfrom the register through a pulse interpolator, contained in thecontroller N, as digital pulses to drive servomotors so that the toolstrace the respective indicated paths in order to regulate the feedspeeds. Prior to the succeeding machining operations the digitaldeviations memorized in the deviation memories are delivered as thepulses to drive servomotors through a gate circuit operable by aprogrammed command from the miscellaneous function device and a pulseinterpolator. Such a gate circuit and pulse interpolator areconventionally contained in such a controller N. The cross slide B isthereby shifted -AX and +AZ equal to the detected deviations to correctthe positioning of the tools.

That is, for instance, in the case of turning or cutting by the tool Bthe co-ordinate axes (X and Z) having an origin or reference point lyingat tip P transfer to new parallel co-ordinate axes (x and z) whoseorigin thus lies at a tip point P Because of this relocation, theworkpiece W can be turned as precisely as previously programmedaccording to the original cutting command signals from the tape readerT. That is, for example, even after the center of rotation of saidworkpiece W is shifted from O to *0, the results of the turned portion Wby the tool B are accurately obtained with the radius r Needless to say,the deviations of the tools due to other than that of relocation of thecenter of rotation, e.g. wear of the tip P setting error, etc., arecompensated by the actuation of the measuring element D to sense theturned portions W W based upon the program, as disclosed in theaforesaid pending application.

FIG. 2 shows diagrammatically the automatic measuring and thetransformation of the co-ordina'te axes in a center work set-upaccording to the present invention. The workpiece W is supported at oneend by a chuck F and at the other end by a center K mounted to a shaft Jof the tail stock I, as shown. It is assumed that the center line of themain spindle S shifts -Ax from O to 0' due to heating of the spindle S,for example, resulting from the continuous turning for an extendedperiod. Since there occurs no thermal deviations in the center K, theaxis of rotation of the Work 'W tilts through Aliabout a center, the tipK of the center K. Accordingly, when the 'WOlk W is turned ormachined'by the tools B B B B which have been previously precisely setin accordance with the program in the tape reader T, said workpiece W isturned to an undesirable conical shape. However, when the tip of thefeeler E of the measuring element D is given a measuring demand signal XR in the X direction (so that it is moved along a route, e.g. thedot-dash line shown in FIG. 2) by the command signals issued from thetape reader T so as to come into contact with the measuring standardposition G of the ring gauge G, the above-mentioned deviation AX isdetected.

The detected deviation outputs of the measuring element D are memorizedas digital values at the designated positions in the deviation memoriescontained in the controller N. Prior to the succeeding cuttingoperations the deviation information AX memorized in the deviationmemories and the dimensional numerical information l +l in Z-axisdirection in the register contained in the controller N are used tocalculate an inclination angle For instance, in the case of the tool Bafter the dimen sional information has been converted based upon theformula, which will be explained in more detail later, according to thedimensional information X and Z, for the tip K of the center \K of thetool tip P and the calculated inclination angle A0, the converteddimensional information is delivered to drive servomotors through thepulse interpolator contained in the controller N, so that the tip P isrotated through the angle A0 about the tip K by shifts of the crossslide B to reach the point P. The point P thus becomes the new origin ofthe tool path to be traced by the tool B FIG. 3 shows diagrammaticallythe rotation of the coordinate axes at the tail stock side of the latheshown in FIG. 2 on an enlarged scale. When the rotation axis of theworkpiece W coincides with the initially set axis 0, the programproceeds with the tip P of the tool B moving along a proper route, e.g.P (O,O)-P (X ,Z P (X ,Z The workpiece W being made with the tip P thushas a shape shown by the dot-dash line. Succeedingly, the feeler E ismoved along a route (e.g. the dotdash line from the measuring origin Ebased upon the measuring demand signals programmed), so that said feelerE comes into contact with the surface W to detect that there is nodeviation between the measured dimension and the demand dimension rcommanded in this instance by the tape reader T.

However, when the rotation axis of the workpiece W shifts to axis 0',the co-ordinate axes (X,Z) must be rotated (as a result of a precedingdetecting operation by feeler B) through the angle A0 about the point K01' the tip of the center K. As a result, the turning proceeds withbasing upon the co-ordinate axes (x,z) along a route, e.g. P P P Paccording to the correction and the initially set program, fed to thecontroller N by the measuring element D and the tape reader T,respectively. This results in the 'workpiece W being turned to have ashape as previously programmed and desired, as shown by the solid lineoutline in FIG. 5.

The measuring origin of the feeler B may also be retated through theangle A0 equal to the rotation angle of the turning origin so that saidfeeler E shifts from the point E to the point E Thus, in measuring, thefeeler E is then moved along the heavy dot-dash line in the directionshown by the arrow to come into contact with the surface of the work Wto now detect whether there is a deviation between the measureddimension and the radius r initially programed, for use on the nextcycle.

In short, the tip P of the tool B in the embodiment shown in FIG. 3 isthe origin of the programed tool path for the tool B and the calculationand conversion of X cos A0+Z sin A0X and Z cos A0-X sin A0-Z are made inthe controller N by the rotation of the center line of the work Wthrough the angle A0, the converted dimensional information is deliveredthrough the pulse interpolator, and the tip P of the tool B is shiftedin X and Y directions according to values equivalent to the aboveconverted values. Thus the origin P of the new tool paths after theangular displacement A0 is determined.

In the succeeding machining operation, whenever the programeddimensional information (X Z (wherein i=2, 2, n) of the tool paths isread by the tape reader T the calculations of X,=X, cos (xX) +Z, cos

/\ (zZ) and Z =X, cos (zX) +Z cos (x2) are carried out 6 in thecontroller N, so that the converted dimensional information (X z(wherein 1:1, 2, n) for the tool paths are delivered to regulate thepaths. Accordingly, the work having a rotation axis with any giveninclination angle A0 is turned out so that it has the shape initiallyprogramed.

In this disclosure, there is shown and described only the preferredembodiments of the invention, but, as aforementioned, it is to beunderstood that the invention is capable of various changes ormodifications within the scope of the inventive concept as expressedherein.

We claim:

1. In a numerically controlled machine tool having a chuck and spindleassembly for supporting a workpiece; a tool slide carrying a pluralityof tools; a measuring element on said tool slide; a tape reader forreading programed command information; and a numerical controllingdevice comprised of a controller for supplying the command informationfrom said tape reader to said tool slide to control the tool paths aswell as the revolution of said spindle of the machine tool the selectionof the tools and their feed speed, and memory means for memorizing asdigital values dimensional deviations measured by the measuring elementmounted on said tool slide; the improvement comprising a ring gaugemounted coaxially on said chuck and spindle assembly having a peripheralsurface and an end surface constituting measuring surfaces in thetransverse and longitudinal directions respectively with respect to thecenter axis of said spindle, said memory means memorizing the deviationsof the center axis of said spindle as signals when the deviations ofsaid measuring surfaces are measured by said measuring element, andmeans for supplying said memorized deviation signals to said tool slideduring succeeding cutting operations for compensating the positions ofsaid tools for detected deviations of the measuring surfaces accordingto the memorized signals.

2. The improvement as claimed in claim 1 wherein said controlling devicecomprises means for causing said measuring element to detect thedeviations of the dimensions of the machined portions of the work fromthe programed values and to memorize said deviations of the workdimensions in said memories, and further comprises means for combiningthe dimensional deviations of the surfaces of said ring gauge and thecommand information for calculating the starting positions of the toolsincluding the deviations of the measuring surfaces of the ring gauge andthe deviations of the machined portions of the work, and for supplyingthe combined informations to said tool slide at the start of cutting.

3. The improvement as claimed in claim 1 further comprising means forcombining the command information and the dimensional deviation of saidsurfaces of said ring gauge for calculating the paths of the toolsduring cutting and for supplying the combined information to said toolslide during cutting.

References Cited UNITED STATES PATENTS 2,831,387 4/1958 Oushinsky82-14.4X

3,181,401 5/1965 Rice et a1. 82-l4.4X

3,191,294 6/1965 Daugherty 82-l4.4X

FOREIGN PATENTS 802,206 10/1958 Great Britain .m --l3 LEONIDAS VLACHOS,Primary Examiner U.S. Cl. X.R.

